1. Field of the Invention
The present invention is related to a polarization controlled angle diffuser, a method of manufacturing such a polarization controlled angle diffuser, and a lithographic system including a controlled angle diffuser. More particularly, the present invention is related to a monolithic polarization controlled angle diffuser and a method of manufacturing such a polarization controlled angle diffuser.
2. Description of Related Art
Diffusers use diffractive elements to control an angle of illumination in a variety of systems, e.g., in a lithographic system. As a critical dimension in micro-lithography continues to be reduced, the effect of polarization on imaging performance in lithographic systems becomes more influential. If these effects are not accounted for, the imaging enhancement expected from using a higher numerical aperture (N.A.) lens system and/or immersion lithography may not be realized. If the polarization state of illumination could be optimized while controlling the angular distribution of the illumination, the adverse affects of the polarization may be minimized.
One solution involves creating an array of micro-optics, each providing a particular angular distribution, arranged at varying orientations, in combination with an array of polarizers arranged at varying orientations. For example, to create quadrupole illumination where the two poles on the vertical axis have a different polarization state than the two poles on the horizontal axis, the micro-optic array would include dipole micro-optics with every other micro-optic oriented to spread the light vertically. A polarization controlling element, such as a half-wave plate, is then diced into similarly sized portions as each micro-optic to create mini-polarizers. These mini-polarizers are then also arranged in an array. A certain orientation of the mini-polarizers is associated with each particular angular distribution of the micro-optics. For this particular example, each micro-optic providing a dipole along an x-axis could be provided with a mini-polarizer having a vertical polarization and each micro-optic providing a dipole along a y-axis could be provided with a mini-polarizer having a horizontal polarization. Accordingly, a quadrupole illumination profile where the vertical and horizontal dipoles have different polarizations is realized.
However, this solution requires assembly of numerous small pieces, e.g., 2 mm, making the solution difficult to implement. Given the size and the number of the pieces being assembled into two corresponding arrays, the possibility of errors in such arrangement is not negligible. Further, the alignment of the micro-optics and mini-polarizers, both linearly and angularly, would need to be maintained to insure proper correspondence of angular distribution and polarization state. Additionally, the diced parts would have edge chips or bevels that would increase scatter and thus decrease efficiency of the part. Any gaps between the elements of the array could increase the amount of light in the zero order, which is typically to be minimized in illumination systems for lithography.